1. Field of the Invention
The present invention relates to a magnetic transfer method for a perpendicular magnetic recording medium, a perpendicular magnetic recording medium and a magnetic recording apparatus, and more particularly to a magnetic transfer method for a perpendicular magnetic recording medium, a perpendicular magnetic recording medium and a magnetic recording apparatus suitable for performing perpendicular magnetic transfer of a magnetic information pattern such as format information onto a magnetic disk used in a hard disk apparatus or the like.
2. Description of the Related Art
In general, in the case of a magnetic disk (hard disk) used in a hard disk drive, which has recently been rapidly spreading, after being delivered from a magnetic disk maker to a drive maker, format information, address information and the like are written thereinto as servo signals before being incorporated in a drive. This writing can be performed by use of a magnetic head, but a method of performing magnetic transfer all at once by use of a master recording medium (master disk) having written thereinto these format information and address information, is more efficient and preferable.
In this magnetic transfer technique, with a master disk and a transfer object medium (slave disk) being in close contact with each other, a magnetic field for transfer is applied to one side or both sides thereof by use of a magnetic field generation device constituted of an electromagnet device or permanent magnet device, whereby magnetic transfer of a magnetization pattern corresponding to information (for example, servo signal) included in the master disk is performed.
Regarding such magnetic transfer, various configurations and techniques have hitherto been proposed (for example, Japanese Patent Application Laid-Open No. 2004-87099 and Japanese Patent Application Laid-Open No. 10-40544). Japanese Patent Application Laid-Open No. 2004-87099 has disclosed an invention of an apparatus which holds master disks by use of a pair of holder units and after supplying a slave disk between a pair of the master disks by use of a robot hand, a magnetic field for transfer is applied while the master disks are pressed against both faces of the slave disk and the slave disk is held between the master disks.
Japanese Patent Application Laid-Open No. 10-40544 has disclosed an invention of a technique by which a magnetic field for transfer is applied while a master disk is pressed against a slave disk, the master disk having on the surface of its substrate a configuration of concaves and convexes corresponding to information signal, the surface of at least the convex part being composed of ferromagnetic material.
Magnetic recording media are classified into: in-plane magnetic recording medium that has magnetization easy axis parallel to the plane of its magnetic layer; and perpendicular magnetic recording medium that has magnetization easy axis in a direction perpendicular to the plane of its magnetic layer. In conventional art, due to difficulty of forming perpendicular magnetization films, in-plane magnetic recording media have usually been used.
On the other hand, the development of perpendicular magnetic recording media and perpendicular magnetic recording methods by which a significant improvement in recording density (an increase in storage capacity) can be expected, has progressed and a large scale introduction thereof into the market in the future has been desired.
Consequently, regarding the above described magnetic transfer, also, there has been a need for a configuration compatible with perpendicular magnetic recording. More specifically, the above described development of magnetic transfer technique has been performed, solely focusing on magnetic transfer to in-plane magnetic recording media; but there has been a need for the development of magnetic transfer technique applicable to perpendicular magnetic recording. Against the background of these circumstances, proposals on perpendicular magnetic transfer have also been made.
As the magnetic transfer technique for perpendicular magnetic recording, there have been known the following two techniques.
One of them is a technique that applies a perpendicular oriented magnetic field for transfer to a master disk and slave disk to perform magnetic transfer, the technique being referred to as “bit printing”. FIGS. 8, 9A, 9B and 9C are diagrams illustrating this technique. FIG. 8 is a cross-sectional view illustrating a process of applying a magnetic field for transfer in a magnetic transfer apparatus; FIGS. 9A, 9B and 9C are cross-sectional views for explaining a basic step of magnetic transfer.
In the magnetic transfer apparatus, when magnetic transfer is performed, after initializing DC magnetization illustrated in FIG. 9A is performed, the slave face (magnetic recording face) of a slave disk 40 can be brought into contact with the information supporting face of a master disk 46 and closely attached thereto by a given pressing force. Then, as illustrated in FIG. 9B, with the slave disk 40 and master disk 46 being in close contact with each other, a magnetic field for transfer is applied by a magnetic field generation device 70. Accordingly, as illustrated in FIG. 9C, magnetization patterns such as servo signal can be transferred and recorded.
In the master disk 46, as described later with reference to FIG. 4, there are formed convex parts 47A, 47A, . . . of concave and convex pattern on its surface; and a magnetic layer 48 is formed on the convex part 47A of concave and convex pattern.
In a magnetic field generation device 70 for applying magnetic field for transfer, there is arranged an electromagnet device including a core 72, wound with a coil 73, and having a gap 71 in a direction of thickness of the slave disk 40 and master disk 46 held by a contacting device; and thus it is possible to apply a magnetic field for transfer having a magnetic force line G perpendicular to the slave disk 40 and master disk 46.
There is provided a rotation device (not illustrated) by which, during the application of magnetic field, while the slave disk 40 and master disk 46 are integrally rotated, a magnetic field for transfer is applied by use of the magnetic field generation device 70 and thus magnetic transfer of transfer information recorded on the master disk 46 can be performed onto the magnetic recording face of the slave disk 40.
The other technique is one that, after initializing DC magnetization of a slave disk 40 is performed by applying a magnetic field in one direction, applies a magnetic field for transfer of a horizontal direction to a master disk and transfer object disk (slave disk) to perform magnetic transfer, the technique being referred to as “edge printing”. FIGS. 1A, 1B, 1C, 2A, 2B and 2C are diagrams for explaining this technique. FIGS. 1A, 1B and 1C are perspective views illustrating a magnetic transfer step; FIGS. 2A, 2B and 2C are cross-sectional views for explaining a basic step of magnetic transfer.
As illustrated in FIG. 1C, in a magnetic field generation device 30 for applying magnetic field for transfer, there is arranged an electromagnet device including a core 32, wound with a coil (not illustrated), and having a gap 31 extending in a radial direction of a slave disk 40 and master disk 46 held by a contacting device; and thus it is possible to generate a magnetic force line G parallel to a track direction to apply a transfer magnetic field. Needless to say, it is possible to use a permanent magnet, instead of the electromagnet.
There is provided a rotation device 36 by which, during applying of magnetic field, while the slave disk 40 and master disk 46 are integrally rotated and made to travel in a direction of the arrow of FIG. 1C relative to a magnetic transfer head 30, a magnetic field for transfer is applied by use of the magnetic transfer head 30 and thus magnetic transfer of transfer information recorded on the master disk 46 can be performed onto the magnetic recording face of the slave disk 40.
FIGS. 2A, 2B, 2C and 2D are as described above, cross-sectional diagrams for explaining a step of magnetic transfer. FIG. 2A illustrates a magnetization state of a magnetic recording layer 40B of the slave disk 40 after unidirectional perpendicular oriented initializing magnetization of the slave disk 40 is performed; FIG. 2B illustrates a step of applying a magnetic field with the master disk 46 and the magnetic recording layer 40B of the slave disk 40 being in close contact with each other; FIG. 2C illustrates a magnetization state of the magnetic recording layer 40B of the slave disk 40 after magnetic transfer; FIG. 2D illustrates a reproduction signal at the time of reproduction of this slave disk 40.
Magnetic transfer is performed as follows. That is, after unidirectional perpendicular magnetization of the magnetic recording layer 40B of the slave disk 40 is as illustrated in FIG. 2A, performed by applying a perpendicular oriented magnetic field as illustrated in FIG. 1A, the face in the magnetic recording layer 40B side of the slave disk 40 is as illustrated in FIG. 1B, brought into close contact with the face in the magnetic layer 48 side of the master disk 46, and thereafter magnetic transfer is performed by use of a leakage flux G produced by applying as illustrated in FIG. 1C, a magnetic field for transfer in a direction parallel to the track face of the slave disk 40.
More specifically, as illustrated in FIG. 2B, when a magnetic field for transfer Hd is applied, leakage flux G corresponding to the configuration pattern of the magnetic layer 48 is generated on the surface of the master disk 46. This leakage flux G contains many components of a direction parallel to the film face of the magnetic layer 48, but has relatively large perpendicular oriented components in the vicinity of both ends of the configuration pattern of the magnetic layer 48. Consequently, a recording magnetization pattern P corresponding to the configuration pattern of the magnetic layer 48 is as illustrated in FIG. 2C, recorded on the magnetic recording layer 40B of the slave disk 40 by the perpendicular oriented component magnetic field of leakage flux G.
Referring to FIG. 2C, while magnetization units magnetically isolated in the perpendicular magnetization film turn upward or downward in a direction such that static energy becomes minimal, magnetization transition area Q seems substantially neutral because each magnetization counteracts each other when viewed macroscopically. Consequently, when reproduction of the slave disk 40 illustrated in FIG. 2C is performed, the reproduction signal has a peak of a vertical direction in the recording magnetization pattern P area as illustrated in FIG. 2D; the reproduction signal turns zero in the magnetization transition area Q. In this way, the magnitude of recording magnetization recorded on the slave disk 40 is large according to the residual magnetization value originally contained in the slave disk 40; the amplitude of reproduction waveform reproduced from such recording magnetization pattern is also as large as that of reproduction signal reproduced from recording magnetization patterns obtained by conventional magnetic head recording.
Also, in the case of perpendicular oriented magnetic field distribution in this configuration, large magnetic field amplitudes of reverse polarity can be obtained in the vicinity of both ends of the magnetic layer 48 pattern. Thus, in this technique, the initializing magnetization process is not indispensable.